Powerex Maha MH-C9000 repair help?

tsmccull

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Have three MH-C9000 chargers and the two oldest have developed one slot each that thinks there's a battery inserted (when there's not) as soon as it completes its power on self-test. Those slots then begin charging at 125 mA and show a small fraction of a volt which, of course, effectively turns my 4-slot chargers into 3-slot chargers. Inserting an actual battery into those slots has no effect at all, they still continue to try to charge at the 125 mA rate and never show the real battery voltage, just that initial fractional voltage. Has anyone seen this before and have any idea which component or components might be causing it? Since those slots are now useless for charging batteries, if someone knows what parts need to be replaced to repair them, I figure I have nothing to lose by trying. Thanks for any help and/or perhaps a schematic, if one exists.
 

TinderBox (UK)

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One slot dying seems seems to be a common problem with this charger, mine would discharge but not charge on one slot, maha gives an two year warranty in the UK but mine was three year old, maha said they could not do a repair but could offer a discount on a replacement, but I decided to buy an Opus C3100 which does nimh and lithium ion cells as well and only cost me £21 when the c9000 is still £50 on what must be getting on for a 10 year old charger.

John


QUOTE=tsmccull;4892890]Have three MH-C9000 chargers and the two oldest have developed one slot each that thinks there's a battery inserted (when there's not) as soon as it completes its power on self-test. Those slots then begin charging at 125 mA and show a small fraction of a volt which, of course, effectively turns my 4-slot chargers into 3-slot chargers. Inserting an actual battery into those slots has no effect at all, they still continue to try to charge at the 125 mA rate and never show the real battery voltage, just that initial fractional voltage. Has anyone seen this before and have any idea which component or components might be causing it? Since those slots are now useless for charging batteries, if someone knows what parts need to be replaced to repair them, I figure I have nothing to lose by trying. Thanks for any help and/or perhaps a schematic, if one exists.[/QUOTE]
 
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MidnightDistortions

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I wonder if someone has opened up the charger to find out if it's an easy fix. For those are stuck with a charger with a dead slot can't really make it much worse or just use the other 3 slots. The Opus is a good option, i really want to get the MC3000 since it's more advanced than the C9000 and also charges Li-ion which i will eventually use, i haven't found one with a carrying case yet, for the price of itbut i haven't looked for very long. I need an 8 cell charger since none of the analyzers are offered in 8 slots. Since you have 3 have you tried opening one up to see what it might be? I know a few people had to open up their La Crosse chargers because they get dirty and may malfunction. Clean all the charger battery contacts up and make sure the board is clean then try to see if that works. Make sure the power cord isn't wearing out or the power connecter is moving around too much. Also see if any of the battery contacts look bent or out of place. That's the best advice i can offer right now. Owning one of these chargers is like owning a Walkman. If something goes wrong with it that can't be fixed, buying a new one is about the only option but if there are slots that still work, 3 is still better than none and you have 10 slots to work with since you have 3 units. Takes up more space and difficult to do 4 cells on one charger.
 

TinderBox (UK)

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Well i took mine apart and checked with an dmm and compared the reading with a faulty slot and a working one, So i swapped some components from a working slot to the faulty slot, but the slot still did not work, and some of the parts took a lot of heat to de-solder, and i spent 9 years soldering pcb`s on my last job so i have a bit of experience.

I kept the psu and dumped the rest.

So i replaced it with an Opus BT-C3100 , and then i bought the king of all slot chargers an SkyRC MC3000.

John.
 

MidnightDistortions

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Well that's not good, maybe a different part was going bad? I would maybe try taking apart a good unit and compare everything to the bad one, but that goes into having to buy another C9000 for the same price. Still it's a good charger, i got mine with a carrying case and a 4 AAA/AA holder so i would buy it again but after the MC3000 which actually looks better than the C9000.
 

TinderBox (UK)

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The Maha C9000 is a good charger (it has a greater choice of charging and discharging ma levels than the Opus BT-C3100), I would buy another one if the price was £25 but not £50

John.
 

J_C

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It all starts with cracking it open and linking good, hi-res pics of the top and bottom of the PCB, 90' angle top-down view oriented the same so comparisons between front and back can be more easily made.

That's no guarantee that anyone will see a problem, but a necessary start without known fixes. You would also need to have some experience troubleshooting with a multimeter which I assume you have, tracing the circuit, making measurements and perhaps desoldering components to test, possibly having a variable power supply handy, and well... it's not worth the time to repair only one, but the information for everyone to be able to repair them is worth more.
 

tsmccull

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Thanks for the comments. I've had it open and looked around, but didn't see anything obvious like cracked traces or board areas which appeared to show excessive heat, so my suspicion is that it's a failed component. One of my units' slots failed at the very instant I put a battery in it to charge, so I'm thinking maybe static electricity blew out one of the parts directly connected to a battery terminal, but I haven't spent the time digging into it yet. Was hoping someone might have a schematic since that would make troubleshooting a lot simpler, but if I get energetic enough, I might give it a try in the blind.
 

J_C

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Schematics are always nice to have, but not nearly as important when there are multiple parallel channels as you can use a multimeter to compare readings between each channel to close in on the faulty component. Worse case is a controller IC channel but could be something as cheap and easy as a blown 4 cent transistor. BUT, it helps a lot to have high quality, high res pictures to aid in tracing the circuit, or magnification and a willingness to trace it out by hand and remember what's what.
 

piligrim

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Feb 21, 2019
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Have three MH-C9000 chargers and the two oldest have developed one slot each that thinks there's a battery inserted (when there's not) as soon as it completes its power on self-test. Those slots then begin charging at 125 mA and show a small fraction of a volt which, of course, effectively turns my 4-slot chargers into 3-slot chargers. Inserting an actual battery into those slots has no effect at all, they still continue to try to charge at the 125 mA rate and never show the real battery voltage, just that initial fractional voltage.

I had the same problem with my charger on slot #1. I was able to figure out the problem, so posting here in hope it will be useful to somebody. I started with checking the resistance in various points of two channels. Soon I found a difference. What happened is that the chip U13 was damaged by ESD resulting in the short circuit between pin 1 and the ground. This caused the charger think that the battery was inserted and the "charging" began. I did not know the exact part# for replacement so I ordered an analog switch SN74LVC1G3157. The package is slightly larger but my friend helped me to replace the chip. Now the charger works fine.
 

Daniel P Ziemba

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I can update, of sort, a post by Piligrim on 21FEB19. There are 8 surface mounted chips labeled B7AF and these chips must fail frequently due to all the people having their charger's stuck saying "125ma" and not operating on one of the channels. In my charger U8 failed (shorted pins 1 to 2). This is connected to the thermistor attached to Ch 4. Replacing the chip with a TI SN74LVC1G3157DCKRG4 SPDT analog switch seems to work fine. If you get this part number the fit, due to the 0.65mm pitch (SC70 case), is perfect. I did some research and found that the TI device markings, should be C55, C5F, C5K, C5R, or C5Z. I paid about $6 for 10 on eBay.
I can find zero information about the original chips labeled B7AF or anyone selling them either. How'd Piligrim figure out a viable substitute? Please let everyone know. Thanks in advance.
 

advhtg

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Feb 10, 2020
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I can update, of sort, a post by Piligrim on 21FEB19. There are 8 surface mounted chips labeled B7AF and these chips must fail frequently due to all the people having their charger's stuck saying "125ma" and not operating on one of the channels. In my charger U8 failed (shorted pins 1 to 2). This is connected to the thermistor attached to Ch 4. Replacing the chip with a TI SN74LVC1G3157DCKRG4 SPDT analog switch seems to work fine. If you get this part number the fit, due to the 0.65mm pitch (SC70 case), is perfect. I did some research and found that the TI device markings, should be C55, C5F, C5K, C5R, or C5Z. I paid about $6 for 10 on eBay.
I can find zero information about the original chips labeled B7AF or anyone selling them either. How'd Piligrim figure out a viable substitute? Please let everyone know. Thanks in advance.

My C9000 fires up, counting 000 to 999 then dies altogether. The 12V power supply is fine though. Does anyone think this is worth investigating further ?
George
 
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